Electrogasdynamic generator method and apparatus



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ELECTROGASDYNAMIC GENERATOR METHOD AND APPARATUS Filed Sept. 22, 1967 l I lI l II I t /)LLV l I LA) 1 ,w I 6: I @MBVM 26 1 I 1 pl i, 24

4 F ll '9- I' CHARGE VOLTAGE SOURCE ATTORNEY United States Patent 3,508,085 ELECTROGASDYNAMIC GENERATOR METHOD AND APPARATUS Jan J. Rosciszewski, San Diego, Calif., assignor to General Dynamics Corporation, San Diego, Calif., a corporation of Delaware Filed Sept. 22, 1967, Ser. No. 669,945 Int. Cl. H02n 3/00 US. Cl. 310- 8 Claims ABSTRACT OF THE DISCLOSURE A device which employs a channel through which a fluid moves charged particles against an electric field to generate electric power. High charge density and thereby efiiciency is maintained by injection of supplemental fluid to prevent the electro-static repulsion of like charges from entrapping the charged particles in the boundary layer.

Background of the invention The demand for electric power has been increasing at such a high rate that conventional techniques of power generation will be inadequate to supply the quantity desired. The inadequacies of present systems include their dependence on cooling water and high quality fuel and their inabiilty to generate EHV direct current. Thus a typical power station is located on a river or ocean front, possibly far from the source of fuel supply and generates relatively low voltage alternating current which cannot be efficiently transmitted long distances. In an attempt to alleviate the deficiencies of prior art power generation systems, systems employing electrogasdynamic principles have been proposed. According to this approach, power is generated by transporting charged particles against an electric field. Such a system would be capable of generating EHV direct current and would not be dependent on the availability of cooling water. The efliciency of such systems to date, however, has been severely limited. The inefiiciency results because it has not been possible to maintain a high charged density in the working fluid over the distance necessary to produce a reasonable pressure drop. The derogation of charge density is produced when the repulsive eifect of like charges on one another, together with normal mixing forces, causes charged particles to reach the walls of their containing channel and become entrapped in the boundary layer. Upon reaching low velocity regions, they are attracted to the opposite pole of the electric field and stream backwards against the main flow.

Summary of the invention In view of the aforementioned disadvantages of prior art generating systems, it is therefore an object of the present invention to provide an electrogasdynamic generator with concentration of charged particles.

Another object of the invention is to provide an electrogasdynamic generator having high system efiiciency.'

A further object of the invention is to provide an electrogasdynamic generator capable of producing extra high voltage direct current.

A still further object of the invention is to provide a method of power generation using electrogasdynamic principles. 1

The electrogasdynamic (EGD) generator of the invention employs a fluid under pressure (e.g., the products of combustion of a coal fired furnace) to force the movement of charged particles through a channel against an electric field. To have an efficient system, a large pressure drop must be developed. Pressure drop can be determined from the formula:

Ap: qE l= qA V where q=charge per unit volume .(coul/m. E =axial electric field (volts/m.) l=length of generator (meters) AV=vo1tage difference along the channel Since E is limited by the breakdown field for the particular gas employed, it can be seen that maximum pressure drop can be obtained from a long channel and high charge density. However, there will be a maximum AV that can be practically employed; for example, 1,000 kv.; therefore, the maximum channel length will also be limited. It follows that improvement in the pressure drop and therefore the efliciency of the system is dependent on the ability to obtain a high charge density. The higher the initial charge density, however, the higher the repulsive forces that tend to force the charged particles to the channel walls where they are no longer forced against the electric field and in fact stream backwards in the boundary layer and become neutralized. The instant invention teaches the use of supplemental fluid injected along the length of the channel to force the charged particles to remain in the core of the channel thereby maintaining their high charged density over long distances. Secondary fluid may be injected, for example, through porous walls of the channel or by spaced openings through which emanate concentrated jets of fluid. The secondary fluid may have a component of velocity perpendicular to the long axis of the channel, thereby forcing the charged particles toward the channels center and preventing them from reaching the boundary layer or may be injected tangentially to minimize the depth of the boundary layer.

Brief description of the drawing Description of the preferred embodiment Referring to FIGURE 1, there is shown a single generator section 10 for the practice of the invention. The channel includes an inlet duct 12, charging section 1-4 and divergent channel generating section 16. The charging section 14 is in the form of a convergent venturi and has charging electrodes 18 which pass through the interior and are connected by terminal 20 to a source of charging voltage (not shown). The inlet portion of the divergent channel has a negative or accelerating electrode 22 around the entire periphery of the channel. Similar electrodes 24 and 26 are located at the channel midpoint and discharge end, respectively. Electrode 24 is a neutral or centertap electrode and electrode 26 is the positive or particle discharging electrode. Spaced between the negative and positive electrodes are a number of fluid injection means or secondary gas inlets 28. In the instant embodiment, these injection means comprise rectangular openings through the channel walls and are arranged at an angle to the perpendicular for reasons to be fully described hereinafter. The openings are widest at the inlet end and become progressively smaller down to the narrowest opening at the discharge end.

The operation of the generator is best understood by reference to its use with a particular source of patricles and high pressure fluid. Since the generator of the invention has particular utility in employing low grade 3 coal reserves as an energy source, its operation Will be described in connection with that use.

A substantially conventional coal fired furnace may be employed to produce high pressure flue gases which include air and combustion products. Burning coal and particularly low grade coal produces a fly ash suspended in the combustion products. This fly ash while normally undesirable can be utilized in the instant generator to supply at least a portion of the particles required to carry the charges. If the normal fly ash particles are not sufficient, additional particles could be obtained, for example, by grinding ash in a fluid jet mill and recirculating the particles. The particle size should be on the order of one micron to carry a high charge density while still having suflicient mass to impede drift to the channel sidewalls under the influence of the space repulsive force.

The charges are suspended in the high pressure flue gas and are channeled through the inlet duct 12 to the charging section 14. Charging in the preferred embodiment is accomplished by the electric field or corona process and employs a plurality of small cross-section wires maintained at a high charge potential on the order of 1,000 to 3,000 kv. per meter. The high charge potential, together with the small cross-section, produces a high electric field strength which is capble of charging the particles in a short period of time to saturation. It should be noted that although electric field charging is employed in the instant embodiment that other methods, such as flame ionization, thermionic emission, photoelectric emission or high energy radiation, can also produce charged particles and these methods could also be used in the process and apparatus of the invention.

Since most eflicient charging takes place with a low speed gas flow, whereas efficient power generation requires a high velocity, the charging section 14 is made venturi-shaped and is a transition zone from low speed to high speed flow. In this manner the charging field is still acting on relatively low speed flow but as the charge density increases, the particles are constrained to a narrower channel so that the breakdown field will not be exceeded.

After charging, the particles under the influence of the gas enter the divergent channel 16. The schematic view of FIGURE 2 shows a plurality of particles 30 which represent the charged fly ash particles. These particles, after passing the negative electrode 22 are both attracted upstream to that electrode and repelled'upstream by the positive electrode 26. The gas flow by collision of the gas molecules with the particles, however, forces the particles downstream against the electrical force, thereby translating the kinetic energy of the gas into electrical energy.

As noted previously, the particles would normally be repelled by their proximity to other particles of like charge and thereby be forced to the walls where their kinetic energy will be dissipated in the boundary layer. In the instant embodiment, however, the unique secondary gas injection process prevents this movement and maintains the particles in a relatively narrow stream spaced from the boundary layer and the channel walls. As can be seen from both FIGURES 1 and 2 the secondary gas injection is accomplished through the rectangular openings 28. The openings are relatively large near the inlet end of the divergent channel since the primary gas pressure is highest there. As the primary gas pressure drops due to the work done against the electrical field, less volume flow is necessary since the higher pressure differential produces a jet of higher kinetic energy and therefore the openings may be smaller. In the instant device the openings are at an angle from the direction perpendicular to the gas flow so as to produce a component of the injected gas velocity in the direction of gas flow. The injected gas therefore forces the charged particles to remain toward the center of the channel, but because of its downstream component does not cause excessive tur- 4 bulence which would cause dispersion of the charged particles.

It should be noted, however, that other angular arangements of the openings are possible within the concept of the invention. For example, perpendicular injection may be desirable in some installations to reduce the quantity of secondary gas required. Further substantially tangential injection may be employed and is effective to reduce the depth of the boundary layer to the point that very few particles would be entrapped. Such tangential injection would take full advantage of the kinetic energy of the injected gas in propelling particles along with the main fiow.

The channel is made divergent, widening toward the outlet end to accommodate the added volume due to the injected gas. In the instant embodiment the relative widths of the inlet and outlet ends may be 3 mm. and 1.9 cm., respectively. The increasing cross-sectional areas is effective to prevent increase of the gas velocity as the supplemental gas is injected. The velocity increase which would otherwise develop is undesirable because it would increase friction losses.

The secondary gas, in the instant embodiment, may be from the same furnace gas source as the primary gas since it need not be at a significantly higher pressure than the initial pressure of the primary gas, or may be relatively cool compressed air to help maintain the channel walls at a temperature below that at which the strength deteriorates. In either case, it is supplied to the openings 28, by a plenum chamber (not shown) which surrounds the channel along the portion from the first to last opening.

The gas discharged from channel directly connected to the furnace retains considerable static pressure and in order that high efiiciencies be obtained, multiple staging is employed. A portion of the discharged gas is directed to one or more downstream channels substantially identical to the channel previously described. This gas is recharged and becomes the primary fluid. The remaining gas is employed as secondary gas in the downstream channels. In this manner pressure drops of 10 atmospheres or more are possible with resultant high efiiciency power generation.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

'1. An electrogasdynamic generator comprising:

a source of high pressure fluid;

charging means for introducing electrically charged particles into said fluid; channel means for connecting said source of high pressure fluid with a region of relatively lower pressure; fluid injection means for injecting fluid through the walls of said channel means to maintain said electrical charges in spaced relation from said walls of said channel means; and

electrode means in said channel for withdrawing power from said generator.

'2. The electrogasdynamic generator of claim 1 wheresaid fluid is a gas.

3. The electrogasdynamic generator of claim 2 wherein: i

said channel means comprises a convergent venturi section and a divergent charging section.

4. The electrogasdynamic generator of claim 3 wheresaid charging means are located in said convergent venturi section.

5. The electrogasdynamic generator of claim 4 where- 5 6 said fluid injection means comprises openings in the 8. The electrogasdynamic generator of claim 7 wherewalls of said charging section; in: said openings communicating with a source of gas said charged particles are approximately one micron under pressure. in diameter.

6. The electrogasdynamic generator of claim 5 where- 5 References Cited said openings are larger at the inlet end of said charging section than at the outlet end thereof. UNITED STATES PATENTS 7. The electrogasdynamic generator of claim 6 where- 3,119,233 1/ 1964 Wafiendorf 0' 02 in; 10 3,211,932 10/1965 Hundstad 3l011 said electrode means comprises first and Second elec- 3,275,860 9/ 19 66 Way 31()-11 trodes, said first electrode being located substan- 3,411,025 4/ 1968 Marks 310-11 tially at the inlet end of said charging section and said second electrode being located substantially at DAVID X. SLINEY, Primary Examiner the outlet end thereof. 

